This special seal tag was developed by Jiraiya so it can be used to suppress the Nine-Tails' influence over Naruto Uzumaki. By applying the seal to Naruto's forehead, the Nine-Tails' chakra and personality recede. Naruto is left fatigued afterwards.

Trivia

The kanji written on the seal is 押 (ō), from the verb 押さえる (osaeru), meaning to suppress, to restrain.